Electric fuse



Dec. 24, 1929. T 'E MURRAY 1,740,698

ELECTRIC FUSE original Filed Dec. 11, 1924 f Mmmm Patented Dec. 24, 1929 UNITED STATES PATENT OFFICE THOMAS E. MURRAY, 0F BROOKLYN, NEW YORK; JOSEPH BRADLEY MURRAY, THOMAS .-E. MURRAY, JR., AND JOHN F. MURRAY, EXEC'UTQRB' Ol' SAID THOMAS E. MURRAY,

DECEASED ELEUTBIC FUSE Application illed December 11,1924, Serial Nc. 755,185. lRenewed larok 5, 1929.

My invention aims to provide certain improvenients in fuses designed particularly for high voltages but applicable also to or-` dinary or low voltages.

localized blowing point. On opposite sidesh of the-'reduced section 2 the strip is encased in heads 3 separated from each other by a slight space. These heads are arranged to act as pistons, fittin in a cylinder preferably composed of "an mner insulating tube 4 of fibre and an outer stronger tube 5 of iron or steel pipe. The ends of the tube are closed by end'pieces 6 with air vent holes 7 therein, the end pieces 6 being mounted on the stri s which, pass out therefrom to the termina s, and the parts beingheld by flanged iron or steel caps 8 screwing onto the outertube 5. The heads of pistons 3 may carry annular packing rings 9 and plates 10 of flexible material ontheir inner ends to make a close lit with the surroundin cylinder, so that the heads will be separate promptly and forcibly when a blowout occurs, and so that no burning gas will leak past them.

When the fuse blows or burns out at the narrow part 2,r the gases generated therein will separate the heads 3 and force them back toward the ends of the fuse, the air escaping through the vents 7. The.heads 3` may be of fibre, heat-treated wood or other suitable material. The vent holes 7 should be of suficie'nt size to prevent the building up of substantial pressures in the ends of the tubes when the heads 3 move outward. For greatest freedom of movement of theheads the end pieces 6 may be omitted as described below in connection with Fig. 5.

To ensure a good grip f the head 3 on the fusible strip the latter may be bent as at 11 in Fig. 2 before being imbedded in the head. Also by. bending the sections of the strip beyond the heads, as shown in Fig. 2, they will yield. more readily to the force exerted.

The chief difficulty involved in the use of fuses on high Voltage circuits is `a tendency casing which produces a piston-like action ensures a wide separation of the ends of the strip after a blow and thus 'further reduces the chances of either establishing or maintaining an arc.- In a previous patent of Thomas E. Murray, Jr., No. 1,120,226,Decem ber 8, 1914, a fuse is shown so arranged that the gas generated upon a blow will force the ends of the two sections apart. A similar arrangement is obtained in the present case, with the addition of'the heads 3 with a confined space between them which will cause the gas pressure to throw theheads violently apart, and with the additional protection provided by the imbedding of the ends of the broken strip-in the heads, and particulalythe crooked shape of the strip in such heads. Preferably, two movable' heads 3 are used as illustrated. But the invention contemplates also cases in which a single movable head is arranged to confine the gases against a fixed abutment instead of a movable abutment such as is constituted by the movable heads illustrated.

The arrangement described may be applied also in the form of a series of heads or pistons located at different points in the length of a fuse strip, as in Fig. 3. The fuse stripl 1 in this case has a number of points 2 of aud site sides of the reduced part of the fuse. These heads are located at successive points in the length of the fuse and are all included in a single casin comprising an inner tube 4 of insulating bre with end pieces, the whole being enclosed in an iron or steel tube 5 with end caps 8. v

The present idea may be combined with that of the patent of Thomas E. Murray, Jr., referred to above, confining the blowing point of the fuse; cr the clear space between the ends of the tube heads 3 may be greater than that illustrated in Fig. 1, giving more room for the blowing action. l Fi 4 illustrates such an arran ement, in W ich the heads 3 are separate by a distance equal to or slightly in excess of the length of the restricted portion of the fuse strip. This is the form of apparatus in which I have made the successful demonstrations referred to hereinafter.- In this figure also I have indicated the omission of the y lates 10 of Fig. .1, these being optional. he distance between the adjacent faces of 'the lplungers is indicated as slightly more than the length of the contracted portion Vof the fuse strip. The blowing point of the fuse element may be determined not only by contracting its Width as illustrated but in 80 various other usual or suitable ways known in the art.

For greater voltages it is desirable to give. to the front ends of the fuse strip section a greater freedom of movement under the impulse of the gas generated. A specific arrangement of this sort is illustrated in my divisional application No. 252,439'fi1ed February 7, 1928. In said divisional application I have also described various modifications and have described and claimed certain features of the invention which are equally applicable to the specific designs illustrated herein.

The head in which the strip is imbedded near the blowing point may be of lvarious other shapes and may be guided in various other casings than the tubular casing illus trated. In fact, it is only essential that the head be arranged to yield underthe pressure of the gas evolved. and that the strip be imbedded therein sufiiciently to prevent the arc from traveling back along the strip.

Though I have described with great particularity of detail certain embodiments of my invention, yet it is not to be understood therefrom that the invention is restricted to -the particular embodiments disclosed. Va rious modifications thereof may be made by those skilled in the art without departure from the invention as defined in the following claims.

1. A fuse comprising a case, having a fuse element with a number ofvblowing points in 05' series with one another, and a ,number of plungers on either side of each blowing oint, whic plun ers arefree to move on the lowing of the se.

'2. A fuse case, 'a fuse element and more than two plungers placed along the fuse element, which plungers are free to move on the rupture of a fuse.

3. A fuse comprising a case, a fuse element having a blowing fpoin a plunger in which the portion of the use e ement near the blowing point is encased with a close fit which limits the possibility of the arcs following the fuse strip, which plun` er also fits the case and anV abutment separate by a slight closed space from the face of said plunger, said plunger and abutment fitting the case so as to confine the gases generated by the blowing of the fuse in said slight closed s ace and to cause the plunger with its enclose portion of the fuse to be moved promptly and swiftly away from the blowing point when the fuse blows.

4. A fuse comprising a case, a fuse element having a blowing point, a plunger engaging the fuse element near the blowing point and fitting the case and an abutment separated by a slight closed space from the face of the plungergso as to confine the gases generated by the`blowing of the fuse and to cause the plunger with its engaged portion of the fuse to be moved promptly and swiftly away from the blowing point when the fuse blows, the case consisting of an inner tube of insulating material reinforced by a metal tube adapted to withstand a high pressure of the confined gases.

5. The fuse of claim 3, the portion of the strip embedded in the plunger being bent in a longitudinal direction so as to increase the difiiculty of the arcs following the fuse strip.

In witness whereof, I havehereunto signed my name.

THOMAS E. MURRAY. 

